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39.1: Convert Sorted Array to Binary Search Tree

/************************************************************************/
            /*       39.1:  Convert Sorted Array to Binary Search Tree                               */
            /************************************************************************/
            /*
             * Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
             *
             * */

 public TreeNode sortedArrayToBST(int[] num)             {                if(num==null|| num.length<1)                {                    return null;                }                return buildhelper(0,num.length-1,num);            }                        private TreeNode buildhelper(int start,int end,int[] num)            {                                if(start>end)                {                    return null;                }                int rootindex=start+(end-start)/2;                TreeNode root=new TreeNode(num[rootindex]);                root.left=buildhelper(start,rootindex-1,num);                root.right=buildhelper(rootindex+1,end,num);                return root;            }            

 

39.1: Convert Sorted Array to Binary Search Tree